1. Field of the Invention
The invention comprises a method for repairing cracked shafts and more particularly a method for repairing cracked shafts using hot isostatic bonding (HIP) processes.
2. Summary of Prior Art
Coupling or drive shafts are common components used in many systems. In one specialized application specifically in boiling water nuclear reactors, main cooling water pumps are coupled to a drive motor by a stainless steel pump drive shaft. Portions of the drive shaft are exposed to cooling water, creating longitudinal temperature gradient along the shaft. This temperature gradient in conjunction with the exposure to the cooling water promotes thermal fatigue and stress corrosion cracking.
Additionally, these drive shafts typically have other apparatus such as balancing mechanisms attached permanently thereto. Such drive shafts are extremely expensive, shafts typically costing multi-million dollars to replace including labor and replacement components. Economic considerations have caused considerable effort to be devoted to the development of a suitable method of repairing such shafts.
Typically, when inspections reveal that thermal or corrosion stress cracking is occurring, attempts are made to machine the surface of the shaft to remove the cracked portions, thus eliminating or reducing further cracking. This process caused the repaired shaft to have a smaller diameter in the region of the crack. Additionally, the repaired shaft would again be subject to the same deterioration as the original shaft when reinstalled in the equipment. These characteristics have led to a need for a repair process which does not change the dimensions of the shaft. If possible, it is also desirable that the repair process reduce the tendency toward thermal and stress corrosion cracking.